I am having a difficult time identifying the parvalbumin interneurons so that I can record from them in hippocampus. I am able to visualize neuronal processes, but I cannot find the soma of the cells. I have attempted different slicing orientations and trying to visualize the acute slices on different microscopes. I know that the recombination has occurred because I can stimulate IPSCs onto CA1 pyramidal cells by flashing the blue light onto the slices.
Hi Aundrea,
The Ai32 line expresses ChR2/EYFP fusion protein in Cre expressing cells. Since it is a fusion protein the EYFP is transferred to the membrane together with the ChR2, and that is why you can see neuropil but very weak somas. To better visualize the somas, you may cross your Ai32 with an Ai9 reporter and get PV cells expressing ChR2/EYFP and tdTomato. An other strategy might be to cross the Ai32 with a GFP mouse line like G42 or B13 (both expressing GFP in PV cells), but in this way you will be exciting the ChR2 while looking for a cell to patch.
Best,
Maximiliano